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M; G. KELLOGG. TELEPHONE CIRCUIT AND-APPARATUS.

No. 605,580. I Patented June 14,1898.

(No Model.) 2 Sheets-Sheet 1.

WITNESSES: INVENTOR WMWM Z i; f

(No Model.) 2 Sheets-Sheet 2.

' I M. G; KELLOGG.

\ TELEPHONE 01301111 AND APPARATUS. I No. 605,580. Patented June 14,1898

I MW

ATTORNE 5 UNITED STATES PATENT OF rcE.

MILO e. KELLOGG, OF OHICA OJILL NOIS, ,ASSIGNOR TO THE KELLOGG SWITCH-BOARD AND SUPPLY COMPANY, or sAME PLACE.

TELEPHONE CIRCUIT AND APPARATUS- SIECIFIGATION forming part of Letters Patent No. 605,580, dated. June 14, 1898.

- Application filed March 23, 1887. Serial No. 232,080. (No model.)

To all whom it may concern.-

' trunk-line circuits.

Be it known that I, MILO G. KELLOGG, a; citizen of the United States, residing at Chicago, inthecounty of Cook and State of Illinois, have invented certain new and useful Improvements in Apparatus for Electrical Communication, of which the following is a specification. I

My invention, relates to telephonic communication or to the transmission and reception of signals telegraphically or to systems in which both are combined, but more specially relates to the former. It consists in a system of multiplex communication which I shall describe and claim in detail; and it consists also in a telephone system which includes two central ofiices,with their lines and apparatus, and trunk-circuits between the central offices, whichcircuits are operated on my improved, multiplex system.

In the accompanying drawings, illustrating my invention, Figures 1 and 2' illustrate two central offices,with their subscribers circuits, switching apparatus, trunk-lines, and translators. Fig. 3 shows in an elementary way my multiplex organization. Fig. 4: shows a plug for a connecting-cord. Fig. 5 shows a rheostat for balancing trun k-line conductors. Fig. 6 shows the preferred construction of my induction-coil. Fig. 7 is another view of either of the central offices.

Each central office has a switchboard. Each switchboard has a spring-jack or similar switch for each subscribers line that centers at the central office and also for each trunk-line circuit between the two offices.

h h h are the spring-jack switches for the subscribers lines, and g g g are the switches for the trunk-line circuits. 7

Z Z are the annunciators for the subscribers lines, and are the annunciators for the 1, 2,3, 5, 6, and 7 are induction-coiltranslators or converters of the construction substantially'as hereinafter described, of which there isone in each central office for each I trunk-line circuit.

O G, D D, E E, and F F are pairs of adjacent trunk-wires which connect the two offices. As will be hereinafter seen, I may obtain in my system of multiple telephony as switch of its trunk-line circuit.

many metallic trunk-line circuits less one as there are trunk-wires between the two ofiices.

With the eight trunk-wires shown I obtain seven metallic trunk-line circuits and employ seven induction-coil translators in each central office, one for each metallic trunk-line circuitj A AA and B are subscribers lines centering in their respective central offices. Lines A A A are grounded at their subscribers stations, and each line B is brought back to its central office and there grounded. i 'Inthe circuit of each subscribers line at hiss'tation may be any usual form of subscribers-station apparatus.

is in its metallic trunk line circuit. The other coil of each translator is grounded on one sideand connected on its other side to the main: line connection of the spring jack The ground connection of the switch is grounded through the annunciator of the trunk -line circuit. The spring-jack switches for all the circuits which enter each central office (subscribers and trunk line circuits) are conveniently placed so that they may readily be connected with each other by means of pairs of switchplugs and cords hereinafter described and which belong to the operatorssystems of con- V necting apparatus.

S S in Figs. 1 and 2 represent the systems of operators connecting apparatus for receiving and answering calls and for making and'clearing out connections and the general conduct of the business. There are two pairs of cords with plugs, switches, keys,an'd clearing-out annunciators for each operators' system shown. More can be added as required.

m m and m m are pairs of plugs with their cords adapted for use with the spring-jacks used.

n n are metallic pieces connected with the ground and on which. the plugs normally rest (or when not in use) and by means of which the cords are normally connected to the ground by means of the metallic strip on the handle of the plug, as more fully shown in Fig. 4:.

p p are looping-in switches.

q q are calling-keys, and s s are clearingout annunciators.

There is one loopingin switch, one callingkey, and one clearing-out annunciator for each pair of plugs with cords.

r is the calling-generator, and t is the operators telephone outfit.

There is one operators telephone outfit for each operators system of connecting apparatus. One calling generator or battery may answer for the whole office. The connections of the systems are substantially as shown. It will be noticed that when the levers of the looping-in switch which belong to a pair of cords are placed on its contact-bolts c 'v the clearing-out annunciator is in the circuit of the cords, and when the levers are on the contact-bolts w w the operators telephone is in the circuit of the cords, and that when the calling-key q of a pair of cords is pressed the callinggenerator is connected to the cord by a leg to ground. It also will be noticed that when one of a pair of plugs is placed in a spring-jack of a circuit there is a complete circuit through the pair of cords to the ground and that the operators telephone or clearing-out annuuciator of the cords is in or out of this circuit as the looping-in switch is in one or the other of its positions. It will also be seen that when the two plugs of a pair are placed in the spring-jacks of two wires or circuits connected through the jacks these wires are disconnected from the ground and are connected together in complete circuit, and the operators telephone or the clearingout an nunciator of the cords is in this circuit as the looping-in switch is in one or the other of its positions.

The operation of the telephone-office system as heretofore indicated may be described as follows: If an operator receives a call on a subscribers annunciat or, she places one plug of a pair of plugs in the spring-jack of the line indicated and, placing the levers of the switch belonging to the pair of plugs 011 the bolts 11' w, finds out by conversation what connection is wanted. If it is for a wire in the same office, she places the other plug of the pair in the spring-jack of the wire wanted and, pressing 011 the key (1, calls on that wire. She then moves the levers of the switch to bolts r 'v, and the subscribers lines are connected together for conversation, with the clearingout annunciator of the pair of plugs in the circuit of the two lines. If the operator, how ever, finds that a subscribers line in the other office is wanted, she places the second plug in the spring-jack of one of the metallic circuits between the two ofiices and, pressing on call ing-key q, connected with the plug, makes an indication on the annunciator 2 of that circuit in the other office. The operator at that office will then place one of the plugs of a pair of plugs in a spring-jack of the circuit indicated and by conversation find out what subscribers line is wanted. She then places the other of the pair of plugs in the spring-jack of the line which is wanted and, pressing on the key (1, corrcspon ding to the plug, calls that line. The two operators before leaving the connection move the switches, so that the levers are on bolts 'U of the switches used. The subscribers are now connected for c011- versation through the medium of their two wires and the pairs of cords, induction-coils, and metallic circuits used. Since a clearingout annunciator is in circuit in each office, clearing-out signals sent from either subscribers station will be received at both offiees. It will be seen that after a subscriber has given an order she may, by holding the telephone to her ear, hear the call as it is repeated to the distant station, and thus know that her call is being attended to and is repeated correctly. The operator at either office may, by moving the looping-in switch, listen to ascertain whether the parties are through their conversation. The circuit from the ground at either office through the primary of the induction-coil, the pair of cords, and the subscribers line to ground may be called a local talk-circuit. The metallic circuit, in which is included the secondaries ot' the two induction-coils, may be called the trunkline circuit. \Vhen conversation or calls pass from one office to the other, the current is translated from the local talking-circuit, in which it originates, by means of its ind uetioncoil into a secondary current in the trunk-line circuit and by means of the induction-coil at the distant office is translated into a tertiary currentin the distant local talking-circuit and is there received on the telephone or annunciator in that circuit.

I have shown the switches as spring-jack switches and have provided each subscribers line and each trunk-line circuit with a springjack switch and a calling-ann unciator at each office at which it is connected. The general working of the business, however, may be modified so as not to require these annunciators or the ground connections of the switches. In that case metallic sockets might be used as the terminals of the lines or trunkline circuits and made to fit the switch-plugs used.

I will now describe the system of multiplex telephony shown in the drawings and which forms a part of my invention. In this part of my invention I use an induction-coil translater of peculiar construction, which I will now describe. Like the ordinary inductioncoil it may have an iron core and two coilsor helices around the core. These coils or helices may or may not have the same length of wire, their preferable lengths being based on the relations of the different apparatus and circuits which are to be used in the system.

One of these Wound around the coil and preferably adjacent to it may be called the primary coil, andj the other coil, also wound around the core and preferably around the primary coil, may be called the secondary coil of the induction-coil. The ends of the coils are led to convenient binding-posts or terminals. I also lead a wire to a convenient binding-post or terminal from the inductive center or central point of induction of the.

secondary coil. The whole may be mounted on a convenient base.

By the inductive center or central point of induction of the secondary coil I mean the point in the coil at which there is an equal posed circuit. Around the primary may be wound for the secondary coil a strand of two wires, which I term twin wires, insulated from each other and of identical diameter andlength and of the diameter and length suitable for the proposed circuit. The inner end of one of these wires (the end at which the winding was begun) may now be joined to the outer end of the other wire, and the point of junction will be the approximate inductive center of the secondary coil. This point may be joined by a wire to its binding-post. or terminal. The other ends of the wires are the terminal wires of the secondary coil, and they may be carried to the two terminal binding-posts of the secondary coil. If it should then be found by experiment that when acurrent, is passed through the primary of the induction-coil the induced electromotive force generated in that part of the secondary of the coil which is between the terminal connected with the approximate inductive center and'one terminal of the coil is greater than that'generated in the rest of the coil, convolutions of the section in which the greater electromotive force is generated may be gradually removed until the electromotive force generated in the part of the coil in one fore, two inductive halves or partsof equal inductance.

, With induction-coils constructed as above described and with current dividing in two parts of equal strength and passing in multiple from the inductive center of the secondary through said inductive halves of the secondary no magnetizing effect will be produced thereby in the core of the coil. This is because for each separate convolution of one of said halves of the secondary coil there is substantially a separate convolution of the otherhalf of the coil, which is the mate to said separate convolution of the first-mentioned coil, (there being substantially as many convolutions in one half as in the other,) and the two convolutions which are thus described as mates are with reference to each other in practically the same position and relation to every portion or point of the core, and inas-.

much as the current in the two convolutions is of the same strength and the current passing through one of them is in the opposite tion. When, therefore, current passes in multiple through the two coils of the secondary thus constructed, practically no lines of force emanate from the secondary coil or pass therefrom to the core to magnetize it or any part thereof, and neither the core nor any part thereof is magnetized by the current which passes in multiple through the two coils of the secondary. When the coils are constructed as above described, each point or portion of each of the two inductive halves or parts of the secondary has a corresponding point or portion which is in equivalently the same position as the other with reference to every point or portion of the core.

It is not necessary in the operation of my system that the resistance in one inductive half, as described above, of the secondary of the induction-coil shall be the same as that of the other inductive half.

Fig. 6 of the drawings shows an inductioncoil as described above. Ct is the core. his the primary and c is the secondary coil, having the two sections wand y. f is the terminal of the inductive center of the secondary coil.

. In Figs. 1 and 2 are shown coils numbered 1, 2, 3, 4t, 5, 6, and 7, which are the same as that shown in Fig. 6, and like parts are indicated by the same letters of reference.

AlthoughI have shown and described one way of sending a current over the two sides of each trunk-circuit in series, I do not intend to limit my invention to this particular arrangement, for it is obvious that to secure many of the advantages of my invention various other arrangements may be adopted for the purpose.

One of the advantages of the construction shown and described is that a separate induction-coil in multiple with the two halves of the secondary coil is rendered unnecessary.

It is therefore obvious that the remaining advantages of my system, or some of them, may be secured by the use of this secondary coil independent of the two halves referred to, or, in fact, by the use of any other appropriate means for sending currents over the aforesaid circuit.

The connections between the trunk-wires and the translators at the two central offices are as follows and as shown in the figures: For instance, the wires 0 C are connected to the terminals of the secondary coils of induction-coils 1 1 in the two offices, and the wires D D are connected to the secondary terminals of induction-coils 2 2 in the two offices. The inductive centers of coils 1 and 2 in the offices are connected, as shown, to the secondary terminals of coils 5 5. It is evident that the four wires thus connected afford three trunk-line metallic circuits between the two offices, the first of which is composed of wires 0 O and the two secondaries of the translators 1 1, the second of which is composed of wires D D and the two secondaries of translators 2 2, and the third of which begins, say, at the inductive centers of translators 5 5 and has for one branch or side one half the secondaries of 5 5 and the derived or parallel circuit from the inductive centers of translators 1 1, including the two wires C G and the circuit connections between the translators, and for the other branch or side the other half of the secondaries 5 5 and the derived or parallel circuit from theinductive centers of translators 2 2, including the wires D D and the circuit connections between the translators. In like manner the wires E E and F F may be connected, as shown, to induction-coil translators 3 3, l 4, and 0 6 of the two offices and afford three more metallic circuits between the two offices. The induction-coils 5 5 and 6 6 in the two offices are connected, as shown, from their inductive centers to the secondary terminals of coils 7 '7 and afford a seventh metallic circuit between the two offices, 0 C D D forming in derived or parallel circuit part of one of its sides or branches, and E E F F forming in derived or parallel circuit part of the other side or branch of the circuit. It is evident that this principle of connecting trunk-lines can be extended to an indefinite extent. \Vith sixteen wires we may obtain fifteen metallic circuits, and with thirty-two wires we may obtain thirty-one metallic circuits, either of which may be used to connect any subscribers line of one exchange with any subscribers line of the other.

For each metallic circuit I provide the 10- cal circuits and switches connected with the primaries of its induction-coils, as shown and heretofore described.

The two conductors between the inductive center of one translator and the inductive center of its corresponding translator in the other office in the system above described may be called branch or derived circuits to each other. The resistances of the two branches or derived circuits connecting theinductive center of one translator with the inductive center of its corresponding translator should be equal,as will appear when I describe the operation of the system. To obtain this equality, I place in each of the branches in each of the ofiices a variable rheostat of he proper scope, by which the operators may adjust and equalize as required the resistance of the branch circuits. I have shown the rheostats in the drawings and have marked them Z Z, &c. Fig. 5 represents in detail one of these rheostats. The rheostat should have a sufficient number of coils of the proper resistance or should be otherwise constructed so that any required resistances to make the proper adjustments may be placed in the different circuits. The resistances could be equalized with rheostats in only one office. They could also be equalized in other ways as, for instance, by having a properly-coin structed rheostat in that branch only which is normally of least resistance. If a rheostat is placed in each branch, it may be found necessary to adjust but one of them to obtain the necessaryequality of resistance in the two branches.

Conversation or calls passing from one local talking circuit to another through a trunk-line circuit will not affect the currents which are passing over any other trunk-line circuit of the system, as will be seen by an examination of the apparatus and connections, as shown and described. Forinstance, if a current is translated from the local talking-circuit of induction-coil translator 1 of either office to the trunk-line circuit of that coil, none of it will pass through coil 5 of either office, because the connection of the coils is made at the inductive center of. each of the secondaries of coils 1 1, and since these points are points of equal potential no current can flow through the coils 5 5 at either office to its trunk-circuit. If a current is translated from the local talking-circuit of coil 5 of either office to its trunk-line circuit, the currents in the branches between the inductive centers of coils 1 will be equal, because the resistances of the branches are equal, and since they pass through the inductive halves of coils 1 in opposite directions their effect on the primaries of coils l is neutralized and not felt in the local talking-circuits connected with them. This results from the fact that the current passing through the two halves of the coils 1 in opposite directions are of equal strength, and the two halves of each of the coils are so wound and placed with reference to each other on the core and primary of the coil that the current passing through one of the halves of the coil completely neutralizes the magnetizing tendency of the current passing through the other half of the coil, and thus the combined IIC effect of the coils is to produce no field of affected either by direct action from the secondary coils or through theagency of the iron core, and the telephone-circuits connected therewith would be entirely unaffected. The same effects occur in that part of theoircuit-in which are the coils 2. In a similar way it will be seen that a current passing to any trunk-line circuit of the system does not affect the conversation of any other trunk-line circuit of the system. It is evident that this would not be so if the resistance of any two corresponding branch circuits were unequal or if the connections of one circuit with another were not made at the inductive centers of the secondary coils.

In Fig. 3 is shown the elementary organization of my multiplex system. This figure shows a metallic circuit and a derived circuit. The telephones M and N may communicate and also the telephones H and K. The telephones N and H, for example, are, however, unable to communicate. In this figure the metallic circuit has two balanced conductors R and T, while the derived circuit may have its two sides unbalanced that is, the side of'the'derived circuit, including inmultiple the two balanced conductors R and T, may not be balanced with the side of the derived circuit including the ground. Instead of the ground another metallic circuitR and T may be substituted;

7 but this would not change the balanced or unbalanced conditions of the two sides of the Y derived circuit. This derived circuit is of a higher series than the metallic circuit. The rule for the balanced circuits may be stated thus: The two sides of all circuits except that of thehighest order or series must be balanced with each other, or, to put it in another way, whenever two or more conductors or sides of a circuit or circuits or combinations thereof are in multiple on one side of a derived circuit those of each seriesmust be interbalanced.

In Figs. 1 and2 the conductors F and F;

must be balanced. The combined conductors E and E must balance the combined conductors F and F.

So, also, the conductors D and D must be balanced, likewise theconductors O O. The combined conductors O and 0' .must also balance the combined conductors D and D, but it is not necessary that the conductors E IE FF should balance the combined conductors O O D D.

r In this specification I have used the term primary coil to denote that coil of the induction-coil translator in which the initial current passes, and the other coil is called the connected to'the local talking-circuits, as de scribed. v

The system of multiplex telephony which I have described would be equally applicable were telephone outfits for stations between which conversation passes connected-permanently in the primary coils of the translators.

In that case it would bea private-line system between the stations connected with -each trunk-line circuit." It is obvious that this multiplex system or parts of it-may be applied to telegraphy as well as to telephony, and, in fact, to all systems in which signals or sounds or intelligence of any kind are transmitted from one point to another. I use the terms transmitter and receiver to designate any kind of instrument or instruments for such a purpose.

. In the induction-coil as herein described the secondary coilis described as being wound with a strand of two wires insulated from each other and of identical diameterand length and the two wires so connected to each other and the circuits that currents of the system pass through them in multiple, and when cur-. rents of equal strength are thus passing the magnetizing effect of each of the two coils composed of said wiresthus wound is neutralized, so that neither the core nor any portion thereof is magnetized by the passing of such currents in multiple, this being due to the fact that for each separate convolution each coil of the secondary has its mate in the other coil of the secondary, which is insubstantially the same relation and position as itself to the core and to every point thereof. It is evident that this construction of the coil by which each convolution of one coil of its secondary has its mate in the othercoil which is in substantially the same relation and po-. sition to every point of the core can be'obtained by other modes of construction than by having the two wires placed in a strand. For instance, the two wires may be wound side by side in each separate layer of windings, or they may be placed in alternate layers over the same portion of the core, care being taken that there are,substantially the same number of convolutions in one coil as in the other similarly placed in the same position withreference-to all portions of the core. --A coil might also be constructed in which all or a part of these methods of windings are employed.

Then the coils are constructed as above described, each point or portion of each of the two inductive halves or parts of the secondary has a corresponding point or portion which is in equivalently the same position as the other with reference to every point or portion of the core. My invention is broad enough to include these and other methods of windings by which substantially the construction of coil herein described is obtained.

It is well known that induction-coils may be constructed without iron cores and yet afford approximately good results with high rates of alternation, as with telephone-currents, the air or other non or semi magnetic material serving as the core. My invention is broad enough to include the use of such coils.

In my system the circuits are in acondition of stable equilibrium. No retardation by magnetization of the cores is offered to the telephone-currents in the derived circuit in this condition of stable equilibrium. Consequently no cross-talk results. If new from any momentary cause, such as an external induced current, the balance of the current in the circuits should be destroyed, the circuits would immediately return to their condition of stable equilibrium. This is due to the fact that if the balance is disturbed and one side of the split secondary of any induction-coil receives momentarily a greater current than the other side magnetic opposition is offered to this increase of current, which will tend to immediately decrease this abnormal current to its original value, and it becomes equal in value to the current in the other half of the coil.

I am aware that heretofore multiplex systems having a scheme of circuits analogous to that herein described have been proposed; but in all such cases such systems have described. the use of two induction-coils, each with a separate core, placed, respectively, in the two sides of the metallic trunk-line circuit, or two secondary windings placed upon opposite ends of a core common to both of them, as well as to the primary coil, which latter arrangement is substantially in effect the same as placing the cores in the firstnamed arrangement end to end. In all such cases, however, the windings produce fields of force and magnetization of the core, resulting in retardation of the currents and unstable equilibrium thereof, and, furthermore, in such proposed systems the neutrality effect of the two induction-coils is contingent not only upon the equality of resistance and inductive power of the two coils, but also on the equality of the resistance of the circuit, which equality is necessary in order to pro duce equal fields of force and magnetization of the core, which condition is one of unstable equilibrium, and as it is practically impossible to maintain such conditions the equilibrium will be destroyed and cross-talk between the multiplex circuits will of necessity result.

I claim as my invention- 1. A metallic circuit between two stations, in which are included the secondary coils of two translators, one at each station, each translator containing a core and a primary coil and a secondary coil each wound around the core, each secondary coil having two parts and having its inductive center determined, and each point or portion of each part having a corresponding point or portion in the other part, which pairs of points or portions are equivalently in the same position with relation to every point or port-ion of the core, in combination with another circuit into which said metallic circuit is connected at the two inductive centers of said translators.

2. A metallic circuit between two stations, in which are included the secondary coils of two translators, one at each station, each translator containing a core and a primary coil and a secondary coil each wound around the core, each secondary coil having two parts and having its inductive center determined, and each point or portion of each part having a corresponding point or portion in the other part, which pairs of points or portions are equivalently in the same position with relation to every point or portion of the core, in combination with another circuit into which said metallic circuit is connected at the two inductive centers of said translators, and rheostat apparatus in said metallic circuit whereby the resistances of the two derived circuits from one of said inductive centers to the other inductive center are made equal.

3. A metallic circuitbctwcen two stations, transmitting and receiving apparatus for respectively transmitting and receiving currents over said circuit, two coils, one at each station, included in said circuit, each coil comprising a core and wound around the core a coil with all its convolutions in the same direction and consisting of two parts, said two parts each having substantially an equal number of convolutions, aml every convolution in one part havingsubstantiallyits mate in the other part; which pairs of convolutions are equivalentlyin the same position and relation with reference to every portion of the core, in combination with another circuit into which said metallic circuit is connected at the two points, respectively, bet-ween said two parts of said coils.

l. A metallic circuit between two stations, transmitting and receiving apparatus for respectively transmitting and receiving currents over said circuit, two coils, one at each station, included in said. circuit, each coil comprising acore and wound around the core a coil with all of its convolutions in thesame direction, and consisting of two parts, said two parts each having substantially an equal number of convolutions and every convolution in one part having substantiallyits mate in the other part, which pairs of convolutions are equivalently in the same position and relation with reference to every portion of the core, in combination with another circuit into which said metallic circuit is connected at the two points, respectively, between said two parts of said coils, and rheostat apparatus in said metallic circuit whereby the resist-anccs of the two derived circuits from one of said points to the other point are made equal. I

5. A metallic circuit between two stat-ions, in which are included the secondary coils of two translators, one at each station, each ICC translator containing a core and a primary coil and a secondary coil each'wound around the core, each secondary coil having two parts and having its inductive center determined, and each point or portionof each part having a corresponding point or portion'in the other.

part, which pairs of points or portions are cquivalentlyin the same position with relation to every point or portion of the core, in combination with another circuit into which said metallic circuit is connected at the two inductive centers of said translators, transmitting apparatus sending varying "currents through the two sides of said metallic circuit in series, and other transmitting apparatus sending at the same time varying currents through said other circuit into which said metallic circuit is connected.

6'. A metallic circuit between two stations, in which are included the secondary coils of two translators, one at each station, reach translator containing a core and a primary coil and a secondary coil each wound around the core, each secondary coil having two parts and having its inductive center determined,

and each point or portion of each part having a corresponding point or portion in the other part, which pairs of points or portions are equivalently in the same position with relation to every point or portion of the core, and the resistance of the two sides or branches of said metallic circuit from one of said inductive centers to the other inductive center being equal, in combination with another circuit into which said metallic circuit is connected at the two inductive centers of said translators, transmitting apparatus sending varying currents through the two sides of said metallic circuitrin series, and other transmitting apparatus sending at the same time varying cu rrent's through said other circuitinto which said metallic circuit is connected.

7. A metallic circuit between two stations,

in which are included two coils, one at each station, each coil having a core and wound around the core a coil with all its convolutions in the same direction and consisting of two parts, said two parts each having substantially an equal number of convolutions, and every convolution in one part having substantially its mate in the other part, which pairs of convolutions are equivalently in the same position and relation with reference to every portion of the core, in combination with another circuit into which said metallic circuit is connected at the two points, respectively, between said two parts of said coils, and the resistances of the two sides or branches of said metallic circuit between said two points being equal, transmitting apparatus sending varying currents through the two sides of said metallic circuit in series, and other transmitting apparatus sending at the same time varying currents through said other circuit into which said metallic circuit is connected.

8. In a telephone system, two stations, a metallic circuit with balanced conductors between] them in which are included the secondary coils of two translators, one translator at each station, each translator containing acore and a primary coil and a secondarycoil each wound around the core, said secondary coil having two parts and said parts having substantially an equal number of convolutions and every convolution in one part having substantially its mate in the other part, which pairs of convolutions are equivalently in the same position and relation with reference to every portion of the core, in combination with another circuit into which said metallic circuit is connected at the two points, respectively, between said two parts of said secondary coils, subscribers lines centering at each of said stations and switching apparatus at each station whereby the subscribers lines centering there may at will be connected into the circuit of the primary of the induction-coil.

9. A metallic circuit between two stations, in which are included the secondary coils of two translators, one at each station,each translator containing a core and a primary coil and a secondary. coil, each secondary coil having two inductive parts permanently fixed and determined, and each point or portion of each part having a corresponding point or portion in the other part, which pairs of points or portions are equivalently in the same position with relation to every point or portion of the core, and the resistances of the two sides or branches from a point between said two parts of the secondary of one coil to a point between said two parts of the secondary of the other coil being such and the coils being so constructed as to number of convolutions that when current passes in branch or derived circuit from one of said points to the other point, the inductive effect of the two parts of the secondaries connected into one ofthe derived circuits, balances and counteracts the inductive effect of the two other parts connected into the other derived circuit and no ing at the same time telephone-currents over said metallic circuit.

IIO

10. A metallic circuit between two stations,

part having a corresponding point or portionin the other part, which pairs of points or portions are equivalently in the same position with relation to every point or portion of the core,and the resistances of the two sidesor branches from a point between said two parts of one coil and a point between said two parts of the other coil being such and the coils being so constructed as to number of convolutions that when current passes in branch or derived circuit from one of said points to the other point the inductive effect of the two parts of the two coils connected into one of the derived circuits balances and counteracts the inductive effect of"; the two other parts connected into the other derived circuit, and no magnetic effect is produced in the core, in combination with another circuit into which said metallic circuit is connected at said two points between said two parts of said two coils, transmitting apparatus sending changing current through said last-mentioned circuit and other transmitting apparatus scndingat the same time telephone-currents over the two sides of said metallic circuit.

MILO G. KELLOGG. \Vitncsses:

WALLACE L. DE Wow, CALVIN DE WoLF. 

